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Fetching REST Data with Loading and Error State
Track loading, data, and error; fetch in an effect, check response.ok, parse JSON, handle catch and finally.
Why react-native-gesture-handler Replaces the Responder System
The JS responder system runs on the JS thread so gestures lag under load; gesture-handler runs recognition natively for smooth, reliable gestures.
Debouncing a Search TextInput with Hooks
Keep input in state, in an effect set a timer that fires the search after a delay, clear the timer on each change so only the final pause triggers the call.
Responsive Layouts with Core React Native APIs
Lean on flexbox, percentage sizing, useWindowDimensions, SafeAreaView, and Platform; recompute on dimension change.
JSI, Fabric, and TurboModules in the New Architecture
JSI gives JS direct synchronous access to native via C++, Fabric is the new renderer, TurboModules lazy-load native modules.
StyleSheet.create and Inline Style Tradeoffs
Styles are JS objects of subset-CSS properties; StyleSheet.create validates them and yields stable references, while inline objects allocate each render.
Limits of OTA Updates and Runtime Versions
OTA ships only JS and assets; native changes need a store build; runtime versions gate compatibility.
Optimizing Slow iOS CI Build Times
Profile the build, cache CocoaPods and DerivedData, use prebuilt frameworks, parallelize, scope to changed work.
Designing a Fastfile for Versioning, match, and Uploads
Lanes bump versions, run match for signing, build with gym and gradle, upload via pilot and supply; secrets come from CI env or a vault.
CI/CD Pipeline for React Native to TestFlight and Play
A triggered workflow installs deps, builds signed artifacts on macOS and Linux runners, uploads via Fastlane to TestFlight and the Play internal track.
Over-the-Air Updates for JavaScript-Only Fixes
Ship a new JS bundle the app downloads at runtime and applies on next launch, with no store review.
Android App Bundles versus Universal APKs
An AAB is an upload format; Play generates per-device APKs via dynamic delivery, shrinking download size.
Managing Per-Environment Configuration in React Native
Use per-environment env files plus build flavors or schemes, inject at build time, keep secrets off the device.
iOS Provisioning Profiles and Signing Certificates
The certificate proves developer identity, the App ID names the app, the profile binds certificate, App ID, and devices.
How do you catch RN performance regressions?
Track TTI, JS and UI thread FPS, and memory; baseline them and gate CI with automated tools like Flashlight, using the React profiler and DevTools to diagnose.
What are the key challenges of setting up Detox E2E?
Maintain separate debug/release build configs, rely on Detox automatic synchronization but tame uncontrolled async like timers and animations, and stabilize CI with headless emulators and retries.
RNTL or Detox for a navigation flow?
RNTL can test navigation logic by rendering the navigator in JS and asserting screen changes; Detox runs the real app for true end-to-end confidence including native transitions.
What does 'test behavior, not implementation' mean?
Query elements the way a user finds them (text, role, label) and assert observable behavior; for a Button, fire press and assert the visible effect, not internal state.
How do you test a component using a native module?
Native code is absent in the Node-based Jest environment, so you mock the module with jest.mock to return fake values, often via the library's provided jest mock.
How do you mock a fetch call in Jest tests?
Replace global fetch with a Jest mock or a library like jest-fetch-mock, return a resolved Promise with a fake Response, and reset mocks between tests.